Prognostic index for patients with parotid carcinoma: external validation using the nationwide 1985-1994 Dutch Head and Neck Oncology Cooperative Group database.

Abstract

Validation of the prognostic indices for the recurrence-free interval of patients with parotid carcinoma, the development of which was described in a previous report, is needed to be confident of their generalizability and justified prospective use. The Dutch Cooperative Group on Head and Neck Cancer database contains 231 patients with parotid carcinoma from six tertiary referral centers who were seen between 1985-1994. This database was used to validate the predictive value of the prognostic indices, PS1 (pretreatment index predicting recurrence) and PS2 (posttreatment index predicting recurrence), in patients with parotid carcinoma. Validation methods included calculation of both indices for each patient, comparison of coefficients, construction of survival curves using the published cutoff points, and calculation of concordance measure C. Wald tests for optimization of scale and weights of the contributing variables, and for possible score improvement by including other variables, were also performed. The 5-year disease-free rate was 62% (standard error = 4%). PS1 was calculated for 183 patients. The previously set cutoff points resulted in 5-year disease-free rates that ranged from 92% (PS1 = 1) to 42% for the least favorable group (PS1 = 4). Concordance measure C was 0.74. The postoperative score, PS2, was calculated for 171 patients. Previous cutoff points resulted in 5-year disease-free rates that ranged from 90% (PS2 = 1) to 40% (PS2 = 4). Concordance measure C was 0.71. Both PS1 and PS2 did not improve using the findings in this independent material. The prognostic indices performed adequately in this validation sample. This finding demonstrates that the prognosis of a parotid carcinoma patient can be quantified by using a weighted combination of the parameters of age, pain, clinical T (cT) classification, clinical N (cN) classification, skin invasion, facial nerve dysfunction, perineural growth, and involved surgical margins. A quantified prognosis, in terms of the recurrence-free interval, can be used to provide information to the patient, to perform clinical trials, and eventually to make clinical decisions. A user-friendly translation and computerized calculation of the indices should be the next step toward generalized prospective use and repetitive evaluation of the indices.